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Earthquakes/ch 19

Earthquakes/ch 19. Earthquake. Earthquake---shaking of Earth’s crust caused by energy release as two lithospheric plates move Elastic Rebound Theory— Friction builds between plates Plates slip as friction is overcome Plates retain shape but have different location. Depth of E.Q.

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Earthquakes/ch 19

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  1. Earthquakes/ch 19

  2. Earthquake • Earthquake---shaking of Earth’s crust caused by energy release as two lithospheric plates move • Elastic Rebound Theory— • Friction builds between plates • Plates slip as friction is overcome • Plates retain shape but have different location

  3. Depth of E.Q. • Depth of E.Q. depends on the boundary type. • A Spreading Centers(mid-ocean ridges)----shallow --- destructive • B) Transform boundary ( San Andreas Fault)---shallow - destructive • C) Subduction zone—deepest E.Q.- least destructive

  4. Earthquakes • Focus----point of first movement.Source of energy ( occurs underground) • Epicenter---point on Earth’s surface directly above the focus ( point of destruction)

  5. E.Q. waves • Earthquake Waves: • 1) P waves---Primary waves • 1st to arrive • Travels in L S and G • Compressional waves • Goes through mantle • Bend in the core • Rocks move in same direction

  6. E.Q. Waves • 2) S-wave—secondary wave • Go through solid only • Cannot travel through outer liquid core of Earth • Arrive second at EQ station • Shearing stress causes this wave • Side to side movement-

  7. E.Q. Waves • 3) L-wave----surface waves • Most destructive waves • Move like ripples across a lake • Ground moves in 2 directions

  8. Two main types of waves: Body waves : those that pass through the body of the medium Surface waves: travel at the surface of the medium

  9. Body waves: • P ---primary • S---secondary

  10. Surface waves: • Love waves: rock moves side to side and perpendicular to energy • Rayleigh waves: move ground with a rolling action

  11. page 301 and draw and label the seismograph diagram

  12. Seismograph Stations • Seismometer—an instrument that records e.q.vibrations. • Seismograph—instrument that detects and records E.Q. waves • Seismic waves---are the main source of information about Earth’s internal structure

  13. Earthquakes • Most E.Q. occur at plate boundaries in narrow seismic belts • 80% of e.q. occur in Circum-Pacific Belt • 15% of e.q. occur in Mediterranean-Asian Belt • All others at mid-ocean ridge

  14. Earthquakes • Locating an Earthquake: Difference in arrival time of P-waves and S-waves is used to determine distance from EQ to station. Use the Time-Travel Graph Info from only 1 station is needed

  15. Time-Travel Graph • Page 275---old textbook • Do a time-travel activity to determine how far the epicenter is from the seismic station • The farther the e.q. is from the station the greater the difference in arrival time of P and S wave

  16. Earthquake Location • Distances from 3 different stations are needed to locate the epicenter • Location activity

  17. Measuring Earthquakes • Richter Scale---measures energy released • Energy released is the magnitude • Richter Scale is 1-10 • Each # represents energy 30X greater than the # before it

  18. Moment magnitude scale: measures EQ strength based on: A) size of area the fault moves B) average distance that fault blocks move C) rigidity of rocks in area This scale is BEST for LARGE earthquakes

  19. The magnitude ( energy released) is best measured by both: Richter and Moment Magnitude Scales

  20. Measuring of E.Q. • Modified Mercalli Scale– I---XII • Measures intensity of EQ • Intensity is the amount of damage done to structures • As the distance between epicenter and EQ increase the intensity decreases • Maximum eq intensity occurs at epicenter • Height of “L wave” determines intensity

  21. Types of stress: • 1) compressional---decreases the volume of a material • 2) tension—pulls a material apart • 3) shearing—causes a material to twist • Stress: --force per unit area acting on a material • Strain---deformation of materials in response to stress

  22. Vocab • Fault---fracture in crust due to stress • Three types of faults: Reverse---compression 1 plate moves up Normal—tension—1 plate moves down Strike-slip—shearing—friction is over come reason roads are broken

  23. Vocab • Tsunami---large, powerful ocean wave generated by the vertical motions of the seafloor during an EQ • Seismic Gap---place along an active fault that has not experienced an EQ for a long time • Moment magnitude scale—scale used to measure EQ magnitude( size of fault, rocks stiffness)

  24. Earthquake Areas • Plate Boundaries---- • San Andreas California • Mid-plate Quakes • New Madrid, Missouri

  25. Measuring EQ • Depth of EQ focus helps determine strength • Shallow focus will cause catastrophic eq and high intensity values • The number of high intensity e.q. is less than the number of low intensity of e.q.

  26. Earthquakes • Shadow Zone---a wide belt that does not receive p-waves, s-waves, or l-waves.. It is an area about 11.000 to 16,000 km from the focus.This is due to the :”p” wave refracting twice as it goes through the outer liquid core. • page 503 ---shadow zone

  27. Earthquakes • Mohorovicic discontinuity Zone—(MOHO) • The boundary between the mantle and crust in which the p and s wave travel at different speeds than at other places on earth. They speed up when move from crust to more dense mantle material. • It occurs : • 32 Km underneath continents • 8 km underneath oceans

  28. Review questions: PP 310-311 # 1-16 and 33-36 Pp 312 and 313 # 1-14

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